1. Field of the Invention
The present invention relates to a process for producing a thermoplastic resin composition which is excellent in mechanical properties, moldability, solvent resistance, low water absorptivity and dimensional stability and at the same time, has a low specific gravity (is lightweight) and a superior mold processability. This resin composition is used as a material for motor vehicle parts or electric or electronic parts.
2. Description of Related Art
Crystalline polyamide resins are being widely used as an industrial material because of their strength and high rigidity, however, these resins are known to have high water absorptivity and therefore, suffer from reduction in rigidity, dimensional stability or the like due to water absorption.
Polyarylene ether, and particularly polyphenylene ether, resins are known as an engineering resin having excellent heat resistance, however, these resins are known to suffer from problems when used alone, such as inferior properties in impact resistance, solvent resistance and moldability.
In order to redeem the defects of these two kinds of resins, Japanese Examined Patent Publication (Kokoku) Nos. 45-997 and 59-41663 have proposed to blend a polyamide resin with a polyphenylene ether resin and the thus-obtained resins are practically used. However, the impact resistance of polyphenylene ether is not sufficiently improved in these techniques and a large number of methods for imparting impact resistance by further adding a rubber-like material to these two resins have been proposed as, for example, in Japanese Unexamined Patent Publication (Kokai) Nos. 56-49753 and 61-204262. However, these compositions exhibit poor ability at the mold-processing because of their high melt viscosity and therefore, cannot be used for molded products having a thin wall.
Furthermore, the polyphenylene ether resin and the polyamide resin are substantially incompatible with each other and therefore, for example, a technique of adding an unsaturated carboxylic acid or a derivative thereof disclosed in Japanese Unexamined Patent Publication No. 56-49753 or a technique of using a polyphenylene ether resin previously modified with an unsaturated carboxylic acid or a derivative thereof disclosed in Japanese Unexamined Patent Publication No. 59-66452 is necessary so as to react a polyphenylene ether resin with a polyamide resin.
However, as the polyphenylene ether resin has a high melt viscosity, when a composition is produced by individually adding a polyphenylene ether resin and an unsaturated carboxylic acid, the polyphenylene ether is gelled during melt-kneading due to shearing heat generation, as a result, an appropriate reaction with the unsaturated carboxylic acid does not proceed and the polyphenylene ether cannot be finely dispersed in the polyamide resin matrix.
The method of using a polyphenylene ether resin previously modified with an unsaturated carboxylic acid has a problem in that since the modification of polyphenylene ether and the melt-kneading with polyamide resin are separately performed, the composition costs are high and, therefore, its use is limited.
Other than these, Japanese unexamined Patent Publication No. 4-372656 discloses a method for producing a melt-kneaded composition of a polyamide resin and a polyphenylene ether resin, however, in this method also, the polyamide resin and the polyphenylene ether resin are independently passed through respective melt-kneading processes and then, the polyphenylene ether resin and the polyamide resin are melt-kneaded to form the composition. Accordingly, the above-described problem is still present.
In Japanese Unexamined Patent Publication No. 9-31324, the present inventors have disclosed a composition having a core/shell structure comprising a polyamide resin, a polyphenylene ether resin previously modified with an unsaturated carboxylic acid, an aromatic vinyl compound-aliphatic hydrocarbon copolymer and a polypropylene-base resin. This composition is excellent in mechanical strength, heat resistance, mold processability, dimensional stability and the like. However, as described above, as the modification of polyphenylene ether and the melt-kneading with polyamide resin are separately performed, the composition costs are high and, therefore, its use is limited.
The present invention has been made to solve the above-described problems in conventional techniques and the object of the present invention is to provide a process for producing a melt-kneaded composition of a polyamide resin and a polyphenylene ether resin, where a resin composition having excellent performance can be industrially produced at a low cost without reducing the mechanical strength and the capabilities, established in conventional techniques, such as processability and dimensional stability.
As a result of extensive investigations to attain this object, the present inventors have found that, in producing a composition by blending a polyamide resin, a polyphenylene ether resin, an aromatic vinyl compound-aliphatic hydrocarbon copolymer and a polyolefin-base resin at a specific ratio, when the polyphenylene ether resin, the aromatic vinyl compound-aliphatic hydrocarbon copolymer and an unsaturated carboxylic acid or a derivative thereof are added from an upstream side of a melt-kneading machine and the polyamide resin is added in the middle of the melt-kneading machine, the composition obtained can solve the above-described problems. The present invention has been accomplished based on this finding.
More specifically, the present invention relates to a process for producing a thermoplastic resin composition, comprising melt-kneading a resin composition containing from 40 to 90 parts by weight of (A) a polyamide resin, from 5 to 50 parts by weight of (B) a polyphenylene ether resin, from 5 to 30 parts by weight of (C) an aromatic vinyl compound-aliphatic hydrocarbon copolymer and from 0 to 30 parts by weight of (D) a polyolefin resin, per 100 parts by weight in total of the components (A), (B), (C) and (D), and further containing from 0.01 to 1.5 parts by weight of (E) an xcex1,xcex2-unsaturated carboxylic acid or a derivative thereof per 100 parts by weight of the component (B), wherein the components (B), (C) and (E) are added from an upstream side of a melt-kneading machine and the component (A) is added in the middle of the melt-kneading machine.